The field of the invention is medical imaging, and particularly, the filtering and enhancement of medical images to improve their visual quality.
The quality of medical images is a function of the imaging modality used and the particular method used to acquire the image data. As a general matter, regardless of the imaging modality used, the quality of medical images can be improved by acquiring redundant data which can be averaged to reduce the effects of random noise. Unfortunately, this solution results in an increased scan time that inconveniences the patient and is expensive. Another approach is to increase the power of the imaging system. In MRI this may take the form of a stronger polarizing field (e.g. 1.5 Tesla instead of 0.5 Tesla), in x-ray systems this can take the form of a higher power x-ray beam, and in ultrasound this may take the form of a more powerful rf amplifier and transducer. These measures drive up the cost of the equipment, and in the case of x-ray, increase the dose of ionizing radiation to the patient.
In addition to random noise, image artifacts can be produced in medical images due to corrupted data acquired during the scan of a patient or due to imperfections in the image reconstruction process. Artifacts produced in the image can take many forms such as streaks, blurring, ghosts and distortion, and will depend on the cause of the artifact and the particular imaging modality used.
A very common cause of image artifacts in medical images, for example, is patient movement during the scan. Numerous methods are used to eliminate such motion artifacts, such as immobilizing the patient, shortening the scan time, cardiac and respiratory gating and breath holding. In other words, there are many methods used to deal with the cause of motion artifacts so that they are reduced or even eliminated.
Unfortunately, there are circumstances in which patient motion will inevitably occur and artifacts will be produced. For example, patient swallowing or subtle movements during a magnetic resonance angiography (MRA) exam of the carotid arteries using a 2D time-of-flight (TOF) pulse sequence can produce streak artifacts in an image reconstructed using a maximum intensity pixel (MIP) projection method. As shown in FIG. 2, such streaks reduce the clinical usefulness of the image and may require that the scan be repeated. Such re-scanning is costly and it is inconvenient and uncomfortable for the patient. In situations where the patient is unable to cooperate in remaining motionless, producing good quality images becomes very problematic with some imaging procedures.